The world took its first concerted step towards getting rid of nuclear weapons today when the UN security council voted unanimously for a resolution on disarmament and non-proliferation.

The summit in New York represented the first time the security council had met to focus on the elimination of nuclear weapons. Barack Obama, who at the same time became the first US president to chair a council session, described the resolution as "historic", saying it "enshrines our shared commitment to the goal of a world without nuclear weapons".

The resolution calls for states with nuclear weapons to continue disarming, to ratify a ban on testing them and to agree a treaty stopping the production of fissile material. In return, non weapons states should accept stronger safeguards designed to stop the spread of nuclear weapons.

The resolution, however, is non-binding, and there are many obstacles to its aspirations becoming reality. Obama faces serious opposition in the Pentagon and the US Congress, which has yet to ratify the test ban.

Meanwhile the world faces two simultaneous proliferation crises: in North Korea, which claims to have built a nuclear arsenal and in Iran, which is alleged to be covertly working towards one. Addressing the council, Gordon Brown argued that the world was "at a decisive moment".

"We face the risks of a new and dangerous era of new state nuclear weapon holders and perhaps even non-state nuclear weapon holders," the prime minister said.

The resolution is aimed at fixing the loopholes in the Non-Proliferation treaty (NPT), which has helped keep the number of states with nuclear weapons in single figures, but which is now in danger of falling apart, as emerging powers lose patience with being kept out of the nuclear club.

The US and Russia are due to sign a treaty in December bringing down the number of their deployed strategic weapons from more than 2,000 each to 1,500. Obama today promised much deeper cuts to follow. In January negotiations are due to start on a treaty banning the production of new weapons-grade fissile material. In May, the NPT comes up for review, and Obama hopes to persuade the US Senate to ratify the test ban soon afterwards. "The next 12 months will be absolutely critical in determining whether this resolution and our overall efforts to stop the spread and use of nuclear weapons are successful," Obama said.

Brown said the next round of US-Russian cuts should involve all types of nuclear weapon - a reference to the short and medium-range weapons still stockpiled in Europe. He said the disarmament round after that should "include all other countries", including Britain.

He said Britain was "determined to play its part in full" and said the decision to reduce the number of submarines in the Trident replacement system from four to three, showed that Britain would "retain only the absolute minimum credible and continuing nuclear deterrent capability".

Russia's president, Dmitry Medvedev, called the UN session "a historic moment, a moment offering a fresh start toward a new future". He added: "This is complicated since the level of mistrust among nations remains too high, but it must be done."

China pushed to have a clause included in today's resolution calling on weapons states to emulate its own "no first use" policy, but the US has long resisted such an undertaking, reserving the right to carry out a pre-emptive strike. But Obama is pressing the Pentagon to consider radical changes to US doctrine to downgrade the role of nuclear weapons.

At today's summit, the Chinese president, Hu Jintao continued to press for a "no first use" agreement and a further undertaking. "All nuclear-weapon states should make an unequivocal commitment of unconditionally not using or threatening to use nuclear weapons against non-nuclear-weapon states," Hu said.

The resolution was widely welcomed by pro-disarmament groups as an important first step. Anne Penketh, the Washington programme director of the British American Security Information Council said: "The 15 members of the security council showed today that they are prepared to co-operate in a way that is free from the cynicism surrounding the agenda for a world free of nuclear weapons. As President Obama said, this is a day to celebrate, and it is to be hoped there will be others."